Process for improving photographic negatives.



ABEL BOULARAN Dir DEVAL, OF PARIS, FRANCE.

PROCESS FOR IMPROVING P HGTOGRAPHIC NEGATIVES.

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No Drawing.

To aZZ whom it may concern Be it known that I, ABEL BOULARAN BIT DEVAL,a citizen'of the Republicof France, and resident tthPflllS 66 Rue PierreChar-r011,

France, have invented a new and useful Process for ImprovingPhotographic Neg tives, which process is fully set forth in thefollowing specification. v

In the photographic as well as in the cinematographic industry itfrequently happens that the negatives obtained cannot be used even afterintensifying, owing to the ographic film.

defectiveconditions in which they were taken, such as insufficientlight, insufficient exposure, etc. Certain negatives however have agreat value, and it is sometimes very important to be able to convert auseless negative into a good one. Bythe expression negative is meanthere an ordinary photographic negative, as well as a cinemat- First ofall, a positive is produced on glass from the had negative by theordinary photographic processes, with or without enlargement. When thepositive print, necessarily a bad one, is dry, it'is intensified by theordinary processes, more particularly by the following: 7

The positive print is dipped in a bath of mercuric chlorid with a slightaddition of sulfuric acid. The broportions can vary, but the followingcan be used :l000 c.- c., water, 20 gms. mercuric chlorid, 10 dropssulfuric acid. a

The positive is left to become completely White. When it is white, it iswashed in running water for about an hour and, with out drying, it isdipped into a very diluted aqueous solution of ammonia; This solutioncan be constituted for instance as follows :-1000 cc. water, 100 c. c.of commercial ammonia preferably of 16 strength.

The positive is left to become as completely black as possible, and isslightly Washed.

After drying the print thus intensified, its front face (the gelatinside) is coated with a layer of bichromated gelatin as thin as possible.The bichromated gelatin used must be very strongly colored by the addition of some unalterable coloring matter, for instance China ink. Theproportions can vary. By way of example, the following may be given 50c. 0. water, 10 gms. gelatin, 0.7 gms. potassium bichromate, 10 gms.China ink.

Specification of Letters Patent.

tails.

Patented Nov. e, 1917.

Application fiiedSeptember 15, 1916. Serial No. 120,246.

The print is left to dry in the dark, protected from dust. After drying,the back (the support side) is exposed to light. 'The time of exposurevaries with the intensity of the source of light used. In the sun, theexposure is completed in half an hour, while in the shade it takes abouttwo hours. The operator alone can of course judge of the necessaryduration of the exposure.

The plate is then developed in hot water or by means of other knownreagents.

The original positive gelatino bromid image is then caused to disappearbydipping the plate into a suitable bath, for instance into a bathformed of an aqueous solution containing potassiumferricyanid and sodiumthiosulfate. As an example, the following proportions mayrbe mentioned2000 c. 0. water, 50 gms. potassium ferricyanid, 50 gms. sodiumthiosulfate. a

The immersion of the plate in the bath is continued until the positivevimage completely disappears. As the positive image fades, there will beseen to appear gradually the negative image previously obtained by theexposure of the layer of bichromated gelatin through the positive image.The plate is not withdrawn from the bath until the'negative imageappears in all its de- In this way an absolutely perfect negative isobtained, which is free from any imperfections of the negativeoriginally used and it can be used for obtaining excellent positivecounter-types by the usual photographic brocesses. It must be howeverpomted out that the negative obtained rep resents the original negativereversed. In order to obtain it reversed again, it is suflicient totreat it, with known means, namely by hardening the gelatin by means offormaldehyde and by turning over the film.

'The latter operation is unnecessary in the case of negatives or filmsintended for obtaining positive prints to be used for projection, for insuch a case the positive print is turned over at the moment ofprojection.

In the process described, it is obvious that if the initial negative isnot available, a had positive print can be used for obtaining anexcellent negative which can be printed by purely photographicprocesses, or by processes based on photography.

The negatives obtained by the process described, have no grain. In fact,colored bichromated gelatin has not any grain in itself. The grain in animage on gelatino-bromid exists in the dark portions and decreases untilfinal disappearance in the pure whites. VVhe-n the image is reversed,the grain of the gelatino-bromid will be in the whites of the new imagewhere it will be invisible, and the dark portions or shadows of the newimage, resulting from the lights in the old one, will have no grain. i

The process applied directly to a negative of any kind, renders itpossible to, convert it. into an excellent positive. This directtransformation of a negative into a positive has not, in practice, thesame importance as the obtaining of a negative, but may be useful incertain cases.

Claims:

1. The herein-described process of improving photographic negatives,which consists in intensifying the negative; printing a silver positivetherefrom on a transparent support; coating the front face of thepositive with a thin layer, of colored bichromated gelatin; drying thecoated print in the dark; exposing the positive to light at itssupportside; developing the negative thereby produced on the bichromatedgelatin layer; immersing the printin a bath to cause the intensifiedsilver image to disappear; and washing and drying the negative.

2. The herein-described process of improving photographic negatives,which consists in intensifying the negative; printing a silver positivetherefrom on a transparent support; coating the front face of thepositive with a thin layer of colored bichromated gelatin; drying thecoated print in the dark; exposing the positive to light at its supportside; developing the negative thereby produced on the bichromatedgelatin layer; immersing the print in an aque-.

one solution containing potassium ferricyanid and sodium thiosulfate tocause the intensified silver image to disappear; and washing and dryingthe negative.

3. The herein-described process of improving photographic negatives,which con- (Zonies of this patent may be obtained for five cents each,by addressing the Commissioner of Patents.

parent support; intensifying it by application of mercuric chloridfollowed by a solution of ammonia; coating the front face of thepositive with a thin layer of colored bichromated gelatin; drying theprint in the dark; exposing the positive to light at its support side;developing the negative thereby produced on the bichromated gelatinlayer in hot water; immersing the print in an aqueous solutioncontaining potassium ferricyanid and sodium thiosulfate to cause theintensified silver image to disappear; washing and drying the negative;hardening the gelatin with formaldehyde; and reversing the film. i

4. The herein-described process of improving photographic negatives,which consists in intensifying the photographic, silver image-bearingbody; coating the front face thereof with a thin layer of coloredbichromated gelatin; drying it in the dark; exposing its back to theaction of light; developing the image thereby produced'on thebichromated gelatin layer; immersing the said body in a bath to causethe intensified silver image to disappear; and thereafter washing;

and drying said body.

5. The herein-described process, of imarovin ohoto raphic ne ativeswhich con- 7 a a a: a

fate to cause the intensified silver image to disappear; and thereafterwashing and drying said body. 7

In testimony whereof I have signed this specification in the presence oftwo subscribing witnesses.

ABEL BOULARAN nrr DEVAL. Witnesses: I

CHAS. P. PnRssLY, JULES Roussnn Washington, 8.,

